All the changelings were expelled from ponyville
Changelings were only effectively banned while Shining Armor's barrier was active which -- wasn't very long at all, actually. It also also really reached the borders of Canterlot. Any Changelings that weren't in Canterlot right at that time were probably not banished.
Even so, Changelings could come back to Canterlot after the wedding since Shining Armor took down his barrier and ultimately moved to be with Cadance.
And yeah, what's up with that Changeling?
Seemed to be Cranky's friend.
Personal Headcanon is that Changelings really do live in Equestria and are tolerated so long as they aren't malicious. They're just disguised as something else most of the time.